Apparatus for electrostatic recording



Sept. 26, 1961 1.. E. WALKUP 3,001,849

APPARATUS FOR ELECTROSTATIC RECORDING Filed July 15, 1958 3 Sheets-Sheet I TRANSMlTTER i sv vl r iH K43 RECEIVER TIMER GATE /'5 HORIZONTAL SWEEP I E I 23 I H l l I l 1 22 I I I I l B RECORDER INVENTOR. Lewis E.Walkup A 7' TORNE Y Sept. 26, 1961 L. E. WALKUP APPARATUS FOR ELECTROSTATIC RECORDING 3 Sfieets-Sheet 2 Filed July 15, 1958 FIG. 3

INVENTOR- Lewis E.Walkup ATTORNEY L. E. WALKUP 3,001,849

Sept. 26, 1961 APPARATUS FOR ELECTROSTATIC RECORDING 3 Sheets-Sheet 3 Filed July 15. 1958 DEVELOPMENT MECHANISM 80 A x o 1 I I l I l a v 1 1. 55

lif 57 FUSER F IG. 4

INVENTOR. Lewis E.Walkup FUSER BY M W M i MW ATTORNEY l tau/41.. labia. A

3,001,849 .APPARATUSFOR ELECTROSTATIC RECORDlNG Lewis E. Walkup',-olumb".us, Ohio, assignor, by mesne The present invention relates to the art of recording intelligence, and more particularly to a method and apparatus for recording such intelligence by means of a cathode ray or electron beam.

Inthe high speed record-in-g of intelligence, particularly facsimile or image recordings, many environments the image intelligence is conveyed to a recording station by electiical transmission wherein the image intelligence is carried inthe'forrn or varying characteristics of electrical transmission denotative of the intelligence. At the recording station suitable means are provided for transducing the electrical transmission into a visual form and reducing the same tore'cord, permanent or transitory as the needs dictate. In many environments the sensing of the intelligence to be transmitted and the transmission thereof, particularly when sensed electronically or optically, may be eiiected with extreme rapidity. However,

the transducing and reduction of the intelligence to visual and recbrd form frequently imposes serious time limitations on the overall system due to the inability of the recording station to acceptthe information at the rate capahilities or the sensing and transmission systems. 7

Electron beam or cathode ray tubes withphosphor screen's, due to their ability to respond essentially instan} taneously to electrical intelligence applied thereto, h e therefore commonly been resorted to as arnea'ris :for trans ducing the electrically transmitted intelligence into visual form. However, the image on the phosphor scfe'ens" of such tubes is transitory, and does not of itseltfatiordfa suitable means for displaying a large amber; of intent gc'nce simultaneously, or a memory or i'r'itellig'e'rice for any significant period of time, particularly if the nature oif the transmitted intelligence is continuously varying. blumer'ous efiort's have been directed to recording: per-ma: nently the transitory images cathode raytubes by various optical photogiaphic methods. For many pur; poses such optical photographic recording is not well adapted, because of the n time delay between exposure and developing of the record, the need for wet developing techniques and equipment, and the sensitivity of optical film to cosmic, nuclear, and other radiation. The foregoing drawbacks of optical photographic recording sys-' tems is particularly apparent in the environment of military radar, where the equipment may be installed in high altitude reconnaissance craft, and-where the need for providing rapid'perman'e'nt recording of the radar intelligence is important. I v x The present invention is directed to recordingof intelligence, particularly facsimile or image intelligence, in the intelligence is transirTt'ted or presented to the re corder in electrical form. The present inventionutili'zes a cathode ray or electron beam as the means fontransducing the electrical intelligence to record form,- thereby taking advantage of the substantially instantaneous response characteristics of such beam. However, rather than utilizing a phosphor screen to convert the intelligeiiee' to visual form with the foregoing attendant limitati ns thereof and disadvant'age's'iii' the ensuing optical photographic recording of the phosphor image, in accordance with the present invention, the beam is utilized to create an electrostatic image on a moving web, and byxerographic techniques, the electrostatic image may be United States J 3,0l,849 Patented Sept. 26, 1961 'inediately and continuously developed into a visual image,

and, if desired, formed into a permanent record.

More particularly, in accordance with the present invention, an electron beam is caused to repetitively traverse' a single line of scan at a desired repetition rate. The target scanned by this beam is chosen from a material which is highly resistive electrically, and is substantially opaque to (i.e., essentially non-transmissive of) the impinging electron beam. With each traverse of the target, the beam deposits: an electron charge on the impinged surface. The quantity of charge deposited along the line of scan on the target may be caused to vary in accordance with variations in the beam current during the traverse, as efiected'b'y electrical intelligence signals fed to the recording station. While one side of the target is thus repetitivelytraversed by the electron beam, a web of dielectric sheet material is fed past and in close proximity to the opposite side of the target. By maintaining the remote side of the web grounded or at a suitable potential diiferonce from the target, the air dielectric between the target and web is disrupted and ionized, resulting in the positive ions traveling to the target, and the negative ions traveling to the web and establishing a corresponding charge thereon. If the web is properly positioned relative to the target, the resultant charge thus induced on the web will constitute a line of charge, and quantity of charge along the length of the line will correspond to the quantity of charge and variations thereof created on the target by the electron beam. 7 Thus, for each traverse of the target, a line of electrostatic charge is induced on the web corresponding to the intelligence fed to the recording station. The rate of movement of the web past the target, and the rate of scan of the target by the electron beam are appropriately correlated to provide on the web a succession of lines of electrostatic charge, which taken together denote the image or facsimile intelligence fed to the recording station. This electrostatic image may be immediately and continuously developed by xerographic means to provide a visual image of the intelligence, and this image may, if desired, be fixed to provide a pennanen-t record.

It is accordingly one object of thepresent invention to provide for the recording of intelligence presented in electrical form. V 1

Another object of the present invention is to provide for the recording of facsimile or image intelligence.

A further object of the present invention is, to provide for the recording of intelligence presented in electrical fborm and transduced to record form by use of an electron eam.

A still further object of the present invention is to pro- Vide for the reduction of intelligence carried as a modulation of an electron beam in record form.

An additional object of the present invention is to provide for the reduction of intelligence carried as a modulation of an electron beam into record form by xerographic means and methods.

Other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of one exemplary specific embodiment of the present invention had in conjunctionwith the accompanying draw- .ings, wherein: p I FIG. 1 is an exemplary presentation of one embodiment of the present invention, showing a radar system in functional block diagram cooperating with an electron Y beam recorder, illustrated schematically;

FIGS.;4 and 5 are schematic showings of a typical Xerograph-ic developing system used in conjunction with the electron beam recorder of the present invention.

As previously indicated, one environment in which it is contemplated that the present invention will findimportant utility is that of recording intelligence derived from a radar scanning system. So far as the present invention is concerned, the particular radar system, or the 1 particular mode of radar scan, is not material. However, in FIG. 1 there is presented schematically an exemplary embodimentof a recorder embodying the principles of the present invention, in conjunction with a functional block diagram of a generalized radar system.

In FIG. 1, the recorder is shown within a dashed line box being fed intelligence from a radar system. The radar. system comprises a transmitter 11, feeding an antenna 12. The reflected energy is transmitted by the antenna through the T-R switch -13, to receiver 14, whose detected output. is fed to the recorder 10 through a gatin-g circuit 15.. Timer 1'6 keyed by the radar transmissions triggers a horizontal sweep circuit 17 for the recorder and the gating circuit to program and synchronize the horizontal sweep sequence of the recorder with the application of the received radar intelligence.

The radar receivedintelligence and horizontal sweep circuit output are applied from circuits 15 and 17 to the recorder. The recorder comprises a cathode ray tube 2 1, whose electron gun and beam control circuits are of conventional design. These include a cathode 22, control grid 23, first and second anodes 24 and 25, electrostatic horizontal deflection plates 26, electrostatic vertical deflection plates 27, and intensifying ring 28, all operated in a conventional manner from a suitable power supply i generally indicated as 29. The output of the radar receiver 14 as passed by the gating circuit 15 is applied to the control grid of the electron gun, and thus controls the electron beam current. The output of the horizontal sweepcirc'uit 17 is applied across the horizontal beam deflection platesf26, and thus controls the electron beam tem, the reflected ener'gy denoting that scan cycle is passed bythe gate 15 and applied to the control grid 23 of the electron gun in tube 21. Simultaneously and in timed relation thereto, the electron beam is caused to effect one scan across the tube target, generally denoted by nu- A meral 31, the vertical deflection plates of the tube being biased to this vertical angle. in the reflected radar energy, which may for example be in the time of receiving the reflected energy or in the The intelligence containedintensitythereof, or both, is utilized to modulate the cur:

rent in the electron beam of tube 21 through operation of the control grid 23. Thus, as determined by the radar intelligence, a varying quantity of charge, or a varying charge pattern, is established along the horizontal scan line on the target 31 for each scan cycle of the electron beam. As will be more fully explained subsequently, from this chargepattern applied to the target 31, acorresponding line of charge pattern is induced on that por- 4 entation and record of the radar intelligence information, such as the topography scanned by the radar system.

Considering in detail the feature of the present invention whereby the lines of charge pattern are induced onto the web 32, reference is had primarily to'FIG. 2 which is an enlarged detailed view oflthe cathodef'ray tube target31 and the immediately adjacent area of web 32. The face 46 of the tube 21' is provided with a horizontal narrow slit 45, preferably not much wider than the electron beam designated by arrows '41. 'The electron beam target is formed by covering the slit 45 with a film of high electrical resistance material such as polyethylene terephthalate. The window thus formed should be essentially impervious to the electrons impinging .thereon from beam 41. As illustrated in FIG. 2, electronsfrom the beam 41 are collected on the inside surface of film or membrane 44. Immediately opposite and exterior of the window slit 45 and membrane '44 there is positioned a mandrel 43 of electrical conducting material which may be grounded as shown, or have a positive potential applied thereto. A negative potential may also be used in which case the bias acts as a gate recording on web 32 only those signals greater than a controlled and predetermined level. Web 32 of dielectric material, such as polyethylene terephthalate aluminized on the surface contacting the mandrel 43, is passed over the tip of the mandrel 43 in intimate electrical contact therewith. 'In

order to' provide uniform f spacing between the window 11111144 and the web 32 over the extent of the window,

4 the window is formed concave with respect to the out-side any'spot on web 3 2jis a function of the charge present on j that portion of the inside surface of window film 44 inimediately oppositethe spot on-web 32 under consideration. Since the charge developed on anyparticular portion of window film 44 is a function ofthe electron beam current impinged thereon, and this in turn is a function of the radar intelligence obtained from the radar system, it

is apparent that for each cycle of scan along'target 31 by beam 41, a line of intelligence is induced across the web, with the variations of intelligence within that line being'de'noted by the variations in charge induced thereon.

An equivalent circuit'diagram of the foregoing window and pickup web is presented in FIG. 3. V denotes'the potential difference between the inside surface of target 31 and the mandrel 43. C is the capacitance of web 32, the air gap is the. spacing 42 between film 44'and web 32,. and C is the'capacitance of window film 44. Since the charges accumulated on either surface of the target or window. sheet must, for good reproduction of the applied intelligence, be removed before the scanning electron beam returns'for its next sweep, each side of C (the target) is provided with a high resistance path to ground,

tion of the web 32 immediately adjacent the target.

Thus, as each successive'line of intelligence, so to speak, is'obtained'fr om the radar system, it is accordingly transduced onto successive lines of the web 32 as the latter is advanced past the target from supply roll 33 to take-up roll 34. At 35 the electrostatic charge pattern thus induced on web 32 is developed by Xerographic means into a visualimage, thereby, providing a visual facsimile pres-- which represents the resistance of the window film 44 and the charge dissipation paths for the electrons and ions collected on the surfaces of the window film. When the potential V is high enough, the air in the gap 42 becomes ionized with the consequent formation of equal amounts of positive and negative charge; The charge, Q, eitherthetotal negative or the total positive charge produced in this ionization can be expressed as:

wherein V is the potential required for electrical break ,down of the air gap, C is'the capacitance of the pickup web 32',"C is the capacitance of the window sli'ee't, and is the total capacitance of the system with the air gap 42 broken down electrically I Considering further the electrical characteristics of the present invention, the potential of charge deposited on the inner surface of the 'target'window 31 may be expressed as where E is the potential of accumulated charge in volts,

Q is the accumulated charge in coulombs,

C is the capacitance of charge area of target window to ground in farads,

i is the electron beam current in amperes, and

t is the charging time of area involved in seconds.

Also,

d*f( o where 7 i is the initial charging current in amperes, and Kt) is some function of time. Substituting Equation 3 into Equation 2,

t fu f( )l (4) The function (t) was determined experimentally for a type 5UP electron gun operated at an acceleration potential of 2400 volts, and found to be when 200 v. E 2000 v.

The capacitance of a 1 mm. diameter charged target window area of a 125 thick polyethylene terephthalate window spaced 38,11. from a 125 thick polyethylene terephthalate pickup web is about 2x10" farad. Substituting this value for C in Equation 7, for an acceleration potential of 2400 volts, an initial current of 45 1. amperes, and an exposure time of 1M. second gives a window potential of slightly more than 1000 volts. Since about 700 volts are required to break down this air gap, there would result an electrostatic image potential of about 150 volts, which is sufficient for xerographic development.

We have found that in order to obtain a disruption of the air gap and resultant induction of the charge onto the pickup web, for a cylindrically shaped target window and pickup mandrel of the nature herein described, the air gap 42 between the window and pickup Web should be in the range of from about 25p. to about 125 There'- fore, defining the general operational parameters of the present invention, from Equations 3 and 4, the components in the expression 'L t C 11 1'0) 1 r where It was previously mentioned that the cylindrical curvature of the target window and mandrel facilitated close positioning of the pickupweb to'the target windowwith good electrical contact between the web and the mandrel.

In addition, this configuration enhances the line resolution on the pickup web, because-it results in concentrating the charge induced on the Web. However, there are practical limitations on makin the radius of curvature too small, because 'a cif'c'ular electronbeam intercepts the cylindrical target surface over an elliptical area in which the charge density at the ends or the major axis of the ellipse are accordingly diminished. Preferably, the radius of curvature of the target window and mandrel should be chosen so that the charge density at the ends of the major axis is not substantially less than 95% of that at the center. This limit to the value of the radius of, curve.- ture of the target and mandrel is, of course, a function ofthe chosen electron beam diameter.

With reference to FIGS. 4 and 5, there is presented the principles of, and an exemplary mechanism for, transducing into visual form the electrostatic image of intelligence induced on web 32 by operation of the electron beam. The thin electrically insulating web 32 drawn from supply roll 33 may be a plastic film, such as polyethylene terephthala'te, polystyrene, celluose acetate, ethyl cellulose, or like sheet material of good insulating properties, and preferably of the order of one or two mils thick; or it may be of paper coated on the working surface with one of these plastics, or with awax; or in some instances thoroughly dry paper or cellophane can be used. As the web 132 is drawn from its roll 33, it first passes through a preliminary charging device 51, where the web is brought surface, where an electrostatic charge pattern depicting the intelligence is induced on the web. The web then enters a development mechanism 35, wherethe electrostatic charge patitcru on the web is rendered visible by theselective application of a finely divided material, such as electroscopic powder, or a liquid ink, or like material. As the webemerges from the developer, the intelligence carried thereon is visually intelligible. Where a permanent record of the intelligence is desired, the web is then passed to fuser57, where the powder is permanently fused to the web, or the ink is dried. As is apparent, if only a transistory presentation of the intelligence is desired, the fuser may be omitted, and instead of a fresh web supply roll, the web may be in the form of an endless belt, with means interposed between the developer 35 and the preliminary charger 5-1, on the return side, to clean the intelligence off the Web.

The purpose of preliminary charger 51 is to establish over the web a uniform electrostatic charge preparatory to receiving the intelligence charge pattern. Charger 51 comprises a housing within which is located an" electrode I 52 coated with a radioactive source of ionizing particles,

. battery of voltage source 53 is preferably one hundred to several hundred volts. By varying the potentiometer setting, one can thus establish a field of either polarity and of adjustable intensity between electrode 52 and web 32.

The alpha or other ionizing particles emitted by the radio-active layer on electrode 52 produce ionization of the air in the chamber 51 into negative and positive ions,

and these ions migrate in opposite directions, depending on their polarity, under the influence of the electrostatic field existing between electrode 52 and plate 54; As ions of onepolarity deposit their charge on web 32, the field becomes altered by the charge on the web until a state of equilibrium is reached, in which the potential of the 'web surface is equal to the potential applied to electrode 52 by the potentiometer. Whether [a small positive potential or negative potential is applied to the web, as conw trolled by the setting of the potentiometer tap, depends on factors subsequently considered. In some instances the electrode 52. may be held 'at. ground potential, in p which case the devicemerely serves to remove incidentally acquired'electrostatic charges from the web in preparation for receiving. the electrostatic intelligence charge pattern. Instead of a radioactive source of ionizing particles, the electrostatic charges may be supplied by corona emission as disclosed, for examplepin U.S. 2,777,957 to L. E. Walkup. With the web 32 thus prepared, it is passed between the electron beam target of the tube 21 and mandrel 43 to receive the intelligence charge pattern, as aforedesoribed. j

The, web 32 carrying the intelligence in electrostatic charge form, passes from intelligence transducing station into the developer 35, shown schematically in FIG. 5.

This device comprises a pair of rollers 60 and 65. Roller "60 includes a central beating shaft 64 carrying a pair of axially spaced disks 62 over which the web edge peripheries pass. Flanges 61 confinethe Web in place on disks 62. The web and disks 62 thus form a hopper in which a supply of electroscopic powder 63 iscontained. It is preferable, although not necessary, that the powder 63 be charged by triboelectric or other means to carry the electrostatic charge opposite from that induced on the web at theytransducing station. The powder adheres in the charged areas to produce a visible presentation ofthe intelligence carried by the web. As the powder 63 is tumbled over the web 32, if the initial preliminary charging of the web at 51 were of a polarity opposite from that at the tube 21, then this background charge on the web would be of the same polarity as the charged powder, and

would assist in repelling the developer powder from this background area. After being developed, the web passes a from roller 60 up over roller 65, and down into fuser 57.

In fuser 57 the webpassesfabout roller 58 where it is heated to a temperature sufficient to fuse the developer powder to the web, or, if ink were used as the developer, to dry the ink thereon, thus forming a permanent visual and" directly readable recond of the intelligence trans-r 'droplets or dry powder particles, as disclosed in U.S.

2,784,109to L. E. Walkup may be used for magnetic brush development described in U.S. 2,791,949 to Simmons and Saul are all operable. A powder cloud development apparatus particularly suited for use as developer' 35 in the present system is the device known as a slot development apparatus more particularly described in U.S. 2,815,734 to C. F. Carlson. Devices such as that described in said U.S. 2,815,734 have been made wherein the development system is limited to inch, thereby making possible almost instantaneous viewing of the developed image. The choice of a particular developing process or apparatus would obviously be dependent on the combination and design limitations imposed in assembling the machine for a particularoperation.

Similarly, the means of permanently afiixing the powder image to the backing material is not critical in the instant invention. Thus, if no permanent imageis desired, after examination of the roll,;the loosely adhering powder 15 8 image may be wiped oi as by a rapidly rotating fur brush and therollreused. ,a permanent record is desired, the powder particles may be rendered adherent to the backing materialby-lieating,

aspreviously' disclosed herein, or by contacting the powder-bearing sheet with the vapors of a, solvent for the marking particles or for a resin coating on theimage receiving member as disclosed for example in U.S.

2,776,907 to C. F. Carlson. Where liquid droplets are used, absorption of the liquid into the capillaries of the backing member or an evaporation of the liquidwould serve to aflix the image to the imagereceivingsheet.

hanced simplicity of construction as compared to the complex pin matrix of the pin tube and the continuous pumping of the cathode ray tube inherent in the Lenard window. (In the Lenard window the membrane is thin enoughrsothat the electron beam passes through the window. Windows which are pervious to electron beams are also pervious to air.) In addition the Lenard window entails very high accelerating voltages in the cathode ray tube and generally has poor resolution due to scattering of the electron beam by the window. Furthermore, the priorart has not recognized the various parameters whose control is essential for dependable operation with high resolution. Thus, in the instant invention for the first time there are disclosed means Whereby the electrostatic image forming process may be accurately controlled for dependable operation with high resolution to thereby directly record intelligence with an electron beam.

From the foregoing detailed exemplary description of the present invention, it will be appreciated that there is presented a method and means for recording electrically transmitted intelligence, utilizing an electron beam as the means of transducing the electrical form of intelligence onto record form, in such manner as the record 'may be rendered visual and permanent, if desired, by usual xerographic techniques. Although the present recording technique has been illustrated in conjunction with a radar system for sensing and presenting the intelligence to be recorded, such is presented only as exemplary of one field of use for the present invention. As will be apparent to those skilled in the art, the present invention may be utilized generally in thefield of recording, and it is not intended that the foregoing description shall be interpreted as limiting the scope of the present invention to radar. Also, other variations, modifications and adaptationsof the present'invention will'be apparent to those skilled in the art, and such as come within the spirit and scope of the appended claims are considered to be embraced by the present invention. I claim:

1. An electron beam recorder comprising a sealed and swabbing with cotton. or b said gun, whereby said web and mandrel are in capaciti've relation to said membrane, and a charge established on said membrane by scanning thereof by said beam will disrupt the air between said membrane and web and thereby induce a line of electrostatic charge on said web in accordance with the electron charge carriedvby said membrane.

2. An electron beam recorder as set forth in claim 1, wherein said membrane is concave from the exterior of said tube, and said mandrel is convex with a radius of curvature substantially equal to that of said membrane.

3. An electron beam recorder as set forth in claim 2, wherein the spacing between said mandrel and membrane is chosen to provide an air gap between said web and 5 the diameter of the electron beam.

References Cited in the file of this patent UNITED STATES PATENTS Ekstrand Feb. 17, 1942 2,283,148 Bruce May 12, 1942 2,716,048 Young Aug. 23, 1955 2,879,422 Borden et a1. Mar. 24, 1959 

